disk management from the command-line, part 1 - the instructional

7/26/2019 Disk Management From the Command-Line, Part 1 - The Instructional

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Disk Management From theCommand-Line, Part 1March 10, 2014

Disk Utility within Mac OS X provides a range of disk

management tools, from erasing and repartitioning

hard disks to restoring images and repairing volumes.

It's a simple way of interacting with attached storageon your Mac.

Beyond this graphical front-end are some powerful

command-line tools that we can use directly. In this

series, we'll look at how to replicate the functionality

of Disk Utility at the command-line.

The following guide will require the use of an external

hard drive which will be erased and partitioned.

Terminology

Apartitionis a logical storage unit located on a hard

disk. A hard disk can contain a single partition, making

use of all the space it contains, or it can be split into

multiple partitions.

In order to store data on a partition, it needs a

filesystem. Once a partition has been formatted, this

combination of partition and filesystem is known as a

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volume.

Here's a USB hard drive that has been split into 16

partitions, all of which will display separately on the

Mac as separate volumes since they've been

formatted, though they are all on the same drive.

Imagine you have a loft apartment that's just four outer

walls. Think of partitioning as putting up dividing walls

to create additional rooms. The more walls you put up,

the more rooms you'll have, but all limited to the total

amount of space you first had available.

But these rooms can't be used yet, not until you decide

what each room will be. Formatting a disk partition is

no different than deciding which room will be the

bedroom or kitchen. At that point, it becomes a

volume.

With the introduction of OS X Lion, your Mac's hard disk

is split into two partitions with two corresponding

volumes. The first is hidden and named Recovery HDfor

OS X Recovery, allowing you to reinstall OS X without

needing any physical media. The second is the more

familiar Macintosh HD.

Benefits of the Command-Line

Disk Uti lity is more than adequate to perform any form

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of disk management for most users. It's also safer than

the command-line, displaying warning dialogs before

proceeding with any potentially destructive functions.

For more experienced users, the command-line offers

a greater level of flexibility and control so that what

would normally require several different interactions

and mouse clicks can be done with just one command.

Disk Information with diskutil

The diskutilcommand provides many of the

features of Disk Utility, from verifying and repairing

volumes to changing partition information.

To view the full list of available options for the

command, enter the commanddiskutil.

Partition Information

Using the listoption will display some basic

information about all available volumes and drives

attached. Within Terminal, enter:

diskutil list

In the following screenshot, you can see both the

Recovery HDand Macintosh HD, both partitions

contained on the Mac's internal hard disk. An external

hard disk is also connected with a volume labeled


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Untitled.

There are some hidden partitions (such as EFI) used for

the purposes of providing drivers and settings during

boot. These aren't volumes since they cannot be

mounted.

Depending on whether you have features such as

FileVault 2 or Fusion Drive, your partition layout might

differ slightly to what is pictured above.

For many of the options within diskutil, it's

necessary to use the disk or partition's Identifier. Using

listwill provide you with this information.

Should you have a number of disks and only want to

view information about a specific one, you can append

the disk identifier to the command:

diskutil list disk2


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The first number represents the physical disk

identifier. The number following the letter "s"

represents the partition number. If a disk has three

partitions, it would follow this convention:

disk2s1

disk2s2disk2s3

In addition to list, you can also use infowith the

corresponding identifier to display even further

information, like so:

diskutil info disk2s1

Verifying and Repairing Volumes

As within Disk Utility, the diskutilcommand can

be used to verify or repair volumes of any errors and is

very straightforward to do using either

verifyVolumeorrepairVolume. These options

don't need the disk identifier, just the volume's name:

If the feedback within Terminal looks familiar, that's

because it's the same information Disk Utility

provides.

diskutil verifyVolume /Volumes/{volum


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Disk permissions can also be verified and repaired

using two similar commands:

Erasing Disks

Erasing disks from the command-line can be a

dangerous process as there aren't any warnings or

confirmations. One typo could lead to irreversible data

loss if there's no backup to restore from. If you're not

familiar with the command-line, Disk Utility is just ascapable.

You can either erase a whole disk which will remove

any partitions stored upon it, or individual volumes

without affecting others.

To erase an entire disk, you'll need the disk identifier,

enter the following, adjusting the disk identifier to suit:

You'll notice this command has a little more going on

than previous ones. The structure of the command is:

Erasing a whole disk will clear any partitions and createa new, single partition, before formatting it as a

volume.

diskutil verifyPermissions /Volumes/{

diskutil eraseDisk JHFS+ Test /dev/{d

diskutil eraseDisk {filesystem} {Name


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Filesystem

You can specify the filesystem to format the partition

in by using any that are supported. The most common

would be JHFS+which is more commonly known as

Mac OS Extended (Journaled).

To find out which filesystems you can use, enter:

diskutil listFilesystems

NameThis simply refers to the name of the volume that will

be created. In this instance, I've just labelled the

volume as "Test".

Disk Identifier

Only the primary part of the identifier (i.e. disk1, disk2,

disk3...) is needed. The additional segment indicating

the partition number is omitted.

Erasing Volumes


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Erasing volumes doesn't erase or affect the entire disk,

only the volume you specify.

Here is an external drive that's partitioned with two

volumes, FirstVolumeand SecondVolume. To erase

SecondVolume, the command is:

The command's structure is almost identical to using

eraseDisk, only that you specify the volume rather

than disk. Should a disk contain multiple volumes, only

the one you specify is altered.

Reformatting VolumesYou'll notice that erasing a volume requires specifying

the filesystem and name. This can be a bit tedious if

you don't actually want to change either of these, but

simply want to erase the contents.

Instead, the reformatoption will erase the contents

of the volume without requiring the filesystem or

name, provided these are to remain unchanged.

Now, the volume will be erased but retain the existing

filesystem and name.

Renaming Volumes

Within the Finder, you can quite easily rename the

volume by selecting it on your desktop and pressing

the Return key, just like you would any file or folder.

Renaming volumes within the Terminal uses a

different method than the renaming of files and folder,

something accomplished by using the command:

Wrapping Up

diskutil eraseVolume JHFS+ New /Volum

diskutil reformat /Volumes/SecondVolu

diskutil rename "{current name of vol


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Disk Management From

the Command-Line, Part 2

Remote System

Monitoring With iStat for

iOS

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We've only scratched the surface ofdiskutilyet

covered quite a lot. While the graphical interface of

Disk Utility can be easier to interact with, a task that

would involve several steps can be accomplished with

just one single command.

In the next part of this series, we'll cover how tomanage partitioning and modify volumes.

You can purchase the complete guide to Disk

Management From the Command-Linethat includes

Building an OS X Triage Driveas an ebook in ePub and

PDF format for just $0.99.

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Thanks for this post, it was very helpful. An

external hard drive that was partially formatted

(tried Mac OS X Extended (Journaled,

Encrypted) and it failed upon attempting to

initiate FileVault) could not be erased via the

Disk Utility UI. Terminal commands from your

post did the trick. Thanks again!

Is there a way to totally wipe a drive? Using

DeployStudio, I have a EFI partition that is

messing up my workflows when I attempt to

reimage a machine again. EFI is at disk0s1, the

first partition where DS attempt to place a

image..

Is there a command to wipe EFI?

Thanks

~David

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David Dingley

A month ago

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